The guide wire of the present invention finds particular use in performing balloon dilatation or other medical procedures where a catheter must be advanced through a narrowing in an artery, a vein or other body passage. Balloon dilatation, alternately known as percutaneous transluminal angioplasty (PTA) or percutaneous transluminal coronary angioplasty (PTCA), is a procedure in which a catheter having a cylindrical balloon mounted at its distal end is inserted into a stenosis or a narrowing in an artery. The balloon is inflated with a pressurized fluid to dilate the stenosis. Once the stenosis has been dilated and normal blood flow has been reestablished, the balloon is deflated and the catheter is withdrawn. A procedure for performing PTCA is described in U.S. Pat. No. 4,195,637, granted to Andreas Gruntzig and Hans Gleichner, the specification of which is hereby incorporated by reference in its entirety. The dilatation catheter described by Gruntzig and Gleichner is known as fixed-tip catheter because it has a short guide wire permanently attached to the distal end of the catheter.
Dr. Gruntzig achieved an 80% clinical success rate in the first 1500 PTCA cases with his fixed-tip dilatation catheter system. In approximately 20% of the cases, however, he did not succeed in dilating the stenosis. The clinical difficulties cited by Dr. Gruntzig included:
1) failure to reach the stenotic lesion with the dilatation catheter, PA1 2) failure to cross the stenosis with the dilatation balloon, PA1 3) failure to dilate the lesion.
Failure to reach the stenosis was typically caused by tortuosity in the coronary arteries or branching of the coronary arteries proximal to the lesion, which could not be negotiated by the catheter. Failure to cross the stenosis with the dilatation catheter could be caused by the deflated balloon catheter being too large in diameter to pass a tight stenosis or too much friction between the balloon catheter and the arterial walls entering the lesion. Failure to dilate the stenosis was caused by the lesion being too resistant to being dilated and the inability of the balloon catheter to achieve high dilating pressures. High resistance to dilation can be caused by a lesion which is calcified or highly fibrotic or by a muscular spasm of the arterial walls. These clinical difficulties spurred Gruntzig and others to improve upon the basic technique of balloon angioplasty.
An improved procedure for performing PTCA is described in U.S. Pat. No. 4,323,071 granted to John B. Simpson and Edward W. Robert, the specification of which is also incorporated herein by reference in its entirety. In this improved technique, the dilatation catheter is made with a guide wire lumen through the entire length of the catheter. The catheter is introduced over a small diameter guide wire which helps to maneuver the catheter through the coronary arteries. A further advance in this over-the-wire technique was the introduction of a steerable guide wire for balloon dilatation procedures, which is described in U.S. Pat. No. 4,545,390 granted to James J. Leary. Further refinements of the steerable guide wire are described in U.S. Pat. No. 4,538,622 granted to Wilfred J. Samson and Ronald G. Williams. The specifications of U.S. Pat. Nos. 4,545,390 and 4,538,622 are hereby incorporated by reference in their entirety. The steerable guide wire allows a balloon catheter to be negotiated through tortuous or branching coronary arteries in order to dilate difficult to reach stenoses. These advances greatly improved the clinical success of the balloon dilatation procedure and allowed the technique to be applied to coronary lesions which were previously unreachable.
The problem of being unable to cross a lesion once it had been reached was also being addressed by various advances in dilatation catheters. The adoption of the over-the-wire technique increased the ability to cross tight lesions because the guide wire could be advanced across the stenosis ahead of the catheter to provide a path for the catheter to follow. Competitors, meanwhile, introduced smaller diameter fixed-tip catheters which had a smoother transition from the guide wire tip to the balloon to make it easier to cross tight stenotic lesions. Other advances which improved the "crossability" of dilatation catheters included the use of more lubricious materials for the catheter and balloon and, later, the addition of lubricious coatings to the outside of the catheter and the guide wire so that they could slip past the lesion with less difficulty.
Another area of advancement in dilatation catheters has been in the improvement of the balloon material itself. These improvements addressed both the ability to cross tight lesions with the balloon and the ability for the balloon to dilate highly resistant stenoses. The progression in balloon materials was from polyvinylchloride to radiation crosslinked polyethylene, then to truly high strength materials such as oriented polyamide or polyethylene terephthalate. One process for producing polyamide balloons is described in U.S. Pat. No. 5,055,024, another for polyethylene terephthalate balloons is described in U.S. Pat. No. 4,490,421. By using high strength materials, greater pressure capacity could be achieved with a lesser wall thickness in the balloons, giving the catheter a lower deflated profile which makes it easier to cross tight stenoses.
Despite these tremendous improvements in dilatation catheters, the choice of whether to use a fixed-tip catheter or an over-the-wire system for balloon angioplasty still involves a compromise in performance. The over-the-wire system allows greater maneuverability of the guide wire and the catheter by the physician and, with newly introduced techniques, it also allows exchange of the balloon catheter while leaving the guide wire in place across the lesion. The advanced fixed-tip catheters, on the other hand, provide a lower deflated profile and a smoother transition from the guide wire tip to the balloon so that even very tightly stenotic lesions can be crossed. One attempt to bridge the compromise between these two approaches is a catheter with a "captive" guide wire described in U.S. Pat. No. 4,616,653, granted to Wilfred J. Samson and Jeffrey S. Frisbie. This catheter provides a lower deflated profile and a fairly smooth balloon transition, while allowing semi-independent maneuvering of the guide wire. However, neither the fixed-tip catheters nor this captive guide wire catheter allow catheter exchanges while the guide wire is left in place.
Catheter exchange has become clinically important in recent years, bolstered by the introduction of extendible guide wires and, more recently, "monorail" or rapid exchange catheters. It is important that new guide wire introductions be capable of being used in conjunction with both of these catheter exchange systems. Examples of extendible guide wires can be found in U.S. Pat. No. 5,133,364, granted to Thomas J. Palermo and Stephen M. Salmon, and U.S. Pat. No. 5,060,660, granted to Richard A. Gambale, and James S. Hunter, U.S. Pat. Nos. 5,031,636, 4,922,923, and 4,917,103, granted to Richard A. Gambale, James F. Crittenden, and James P. Ryan, U.S. Pat. No. 4,875,489 granted to Kirsten L. Messner, Robert M. Abrahms, and Ray R. Beitelia, and U.S. Pat. No. 4,827,941 granted to Taylor et al., the specifications of which are hereby incorporated by reference in their entirety. Examples of rapid exchange catheters can be found in U.S. Pat. No. 4,762,129, granted to Tassilo Bonzel, U.S. Pat. No. 4,988,356, granted to James F. Crittenden, U.S. Pat. No. 4,748,982 granted to Michael J. Horzewski and Paul G. Yock, and U.S. Pat. Nos. 5,040,548 and 5,061,273 granted to Paul G. Yock, the specifications of which are also hereby incorporated by reference in their entirety. Rapid exchange catheters such as those described in these patents often have the drawback that they lack the same level of "pushability" as true over-the-wire catheters which makes them more difficult to push across tightly stenotic lesions.
Another related drawback of the current over-the-wire balloon dilatation catheter systems is that the transition between the guide wire and the distal tip of the catheter presents a step, which not only makes it difficult to cross the lesion as previously mentioned, but also can scrape or gouge the atherosclerotic material in the lesion or the arterial wall. One consequence of this can be dissection of the arterial wall. Another possible consequence can be embolization of particles of the atherosclerotic material from the lesion or scraping the endothelium from the artery wall as the catheter passes. Irritating the artery wall by scraping can cause a muscular spasm of the artery walls which can interfere with the catheterization or cause a reduction in blood flow which exacerbates the patient's condition. It has also been theorized that removing the endothelium from the artery walls creates a new site for growth of atherosclerotic plaque or medial hyperplasia which can further compromise blood flow through the arteries. The present invention provides an improved guide wire and a technique for its use which seek to eliminate the compromises in performance involved in using an over-the-wire balloon dilatation system.